Manipulating layer charge to regulate the hydration and swelling of montmorillonite

An experimental investigation was conducted to uncover how artificial manipulation of the layer charge of montmorillonite regulates its swelling and hydration behaviour, and thereby to find its novel applications such as carbon dioxide capture. Charge-reduced montmorillonites (CRMs) were prepared by way of the Li-fixation technique, followed by characterisation of their diverse physical, chemical, hydration and swelling properties, including Atterberg limits, cation exchange capacity, water adsorption isotherms, basal spacing variability and the fraction of expandable layers. Results show that the number of expandable 2:1 layers in a CRM quasicrystal decreases with layer charge, primarily because of the migration of the interlayer Li+ cations into the empty octahedra and hence the reduction in the population of hydrated exchangeable interlayer cations. Also, Li-fixation leads to the conversion of the original expandable 2:1 smectite layers to the non-expendable, hydrophobic pyrophyllite-like layers. Upon Li-fixation, the water retention and adsorption capability of the CRMs decrease gradually with layer charge, while the maximum water content and area of the wetting–drying hysteresis loop of adsorption/desorption isotherms exhibit the opposite trend. Furthermore, a simple method for determining the proportion of expandable layers is developed for the Li-fixed CRMs. The viable application of CRMs for enhanced carbon dioxide capture or adsorption is envisioned in terms of the reduced layer charges and creation of local hydrophobic microzones on the siloxane surfaces.